The generation of energy from solar radiation is an industry in continuous development. There are a great number of solar receiver typologies, but all of them are based on a fundamental premise: the greater the solar radiation captured, the greater the amount of energy produced.
There are two main types of technologies: solar thermal and photovoltaic. The solar thermal is based on the concept of the concentration of solar radiation to produce vapor or hot air, which can subsequently be used in conventional electric power plants. Photovoltaic technology is based on the photoelectric effect for the production of electricity.
Within the solar thermal technology, there are two large groups of concentrators: point focus and linear. Within the point focus concentrators are parabolic dish concentrators and central tower concentrators, the latter surrounded by heliostats that concentrate the solar light on them. Within the linear technology, the Parabolic Cylinder Concentrator (PCC) is the most developed concentration system and currently new Linear Fresnel Collector (FLC) types are beginning to emerge, which also use mirrors to reflect the solar light.
The majority of these systems, whether parabolic dish concentrators, heliostats, cylindrical parabolic collectors or photovoltaic modules, use a tracker system that allows them to remain permanently oriented towards the sun, thus increasing the amount of energy produced.
The solar trackers, in the majority of cases, perform both azimuthal and zenithal tracking and are operated thanks to oleo-hydraulic cylinder circuits.
There are a great number of documents that describe diverse developments of this type of trackers, such as the patents ES2329854, ES2322527, W02008/096029 . . .
This type of operation poses a serious problem: the oil is not an incompressible fluid. This leads to light movements being produced, which, although for the majority of industrial applications, do not pose a problem to take into consideration, in the case of solar concentration, is the cause of a significant decrease in the efficiency of the systems.
The change of volume with respect to the initial volume that the oil experiences upon a change of pressure is known as compressibility constant. In mineral oils, the value of this constant is approximately 1.5 GPa, reducing the volume of around 0.7% for every 100 bars of pressure.
  K  =            -                        Δ          ⁢                                          ⁢          P                          (                                    Δ              ⁢                                                          ⁢              V                        V                    )                      ⁢                  ⁢          (              At        ⁢                                  ⁢        constant        ⁢                                  ⁢        temperature            )      
This constant also depends on the initial pressure and temperature of the oil, increasing its value the greater the initial pressure and the lower the temperature.
Moreover, in cylinders, and in terms of absolute values, the volume of oil can be compressed less the lesser the diameter of the cylinder and thereby its volume.
In trackers, the changes in volume of oil are due to the action of external forces such as the wind and the weight of the tracker itself.
All of this means that in cylinders of 883 mm in length, such as those used in certain trackers, the movement produced as a consequence of the compression is of 6 mm.
In the case of cylinders that regulate the orientation towards the sun such as those used in solar technology, a loss of precision implies a considerable reduction in the efficiency of the system. A deviation in the movement of around 6 mm can bring about losses of up to 100% in a given case.
A possible solution consists in using systems that externally stop the cylinder (rod brakes), if these systems present the limitation that, not being designed for a lot of movement maneuvers, the cylinders are damaged after frequent and prolonged usage. In the case of solar trackers the application is quite different, since it requires a great amount of brake usage maneuvers. Caliper brakes can also be used, but this solution implies a high cost which does not compensate for the efficiency gain.
Therefore, the present invention has the objective of providing a solution to the problem of precision loss due to the compression of oil, achieving an increase in the rigidity of the system without implying a considerable increase in costs.